Surgical microscopes are optical reflected-light microscopes designed for use in medical surgery and providing a magnification typically in the range from 5×-30×. Compared to other optical reflected-light microscopes, surgical microscopes use an objective having an enlarged focal distance of typically between 175 mm and 550 mm and a correspondingly large working distance (distance between the lens vertex of the objective lens of a surgical microscope located closest to an object to be imaged and the object) of typically between 200 mm and 500 mm. For providing a user with a three-dimensional impression of an object to be imaged, surgical microscopes are often configured as stereoscopic microscopes (also referred to as stereo microscopes) providing a pair of optical imaging paths for the eyes of a user, with the optical imaging paths intersecting close to a focal plane of the surgical microscope at a stereoscopic angle of typically between 3° and 14°. The field of view of surgical microscopes, i.e. the area located in the focal plane that can be imaged at a given time by the at least one optical imaging path onto the retina of a user, is typically larger than 1 mm2. The field of view of a surgical microscope thus not only comprises a single image point as is the case with scanning microscopes; rather a multi-dimensional (two or three-dimensional) imaging of the object observed takes place at any point in time. Surgical microscopes are often equipped with a zoom system or a magnification changer for enabling a change in magnification, and a focusing system for changing the working distance. Regular fields of application are surgery and microsurgery.
In surgical microscopes, the image of an object imaged with the operation microscope is alternatively provided to a user by an eyepiece (or in stereoscopic surgical microscopes by a pair of eyepieces), or the image is converted in electrical signals using an image converter (or in stereoscopic surgical microscopes using a stereo image converter or a pair of image converters), and is displayed to the user in addition or alternatively to the eyepieces by at least one of a monitor and a head-mounted display.
Surgical microscopes are often supported by stands mounted to a floor or a ceiling of a treatment room or can be positioned freely across the floor of the treatment room. The stand may be adjustable manually by use of motors, and allows desired positioning and orientation of the surgical microscope above the object to be imaged.
In addition to surgical microscopes, also monoscopical overview cameras having no or only little magnification at a working distance of typically 1,000 mm are frequently used during medical surgery. The simultaneous provision of an overview camera in addition to a surgical microscope increases complexity, since there are two different tools to be handled, and increases cost, since two different tools need to be procured and maintained.
Despite the larger working distance as compared to conventional reflected-light microscopes, the range of working distances achieved with common surgical microscopes is unsatisfactory.